This invention relates to an airship employing the vectored thrust obtained from thrust producing rotor systems affixed to the aerostat hull of the airship as a means of providing dynamic lift, translational movement of the airship and the application of control forces establishing the desired attitude of the airship in flight and in hover.
Although airplane payloads for long-haul transportation have increased steadily in recent years, there is a growing need for the vertical lifting of large payloads over short distances, particularly payloads comprising single integrated structures of relatively large dimensions, such as power plant assemblies, boilers, transformers, atomic power components, pre-fabricated structures, etc. Helicopters have been utilized for the vertical lift short-haul operations but the size payload that can be lifted by a helicopter is limited. The commercial helicopter having the largest capacity available today will lift a load of 10 tons. Larger helicopters are under development of which one has a lifting capacity of 18 tons. However, there is a growing need for transporting large indivisible loads of 25 to 100 tons or more over routes in which vertical airlift capability to lift these loads is the only feasible mode of transportation. Increasing vertical lift capability through rigidly connecting together several helicopters in the manner of U.S. Pat. No. 3,656,723 appears to be feasible. However, the lifting capability of such multiple helicopter lift systems, utilizing presently available or projected helicopters, still falls considerably short of present and predicted vertical load requirements. Since the payload/gross weight ratio of aerodynamically supported vehicles diminishes with increase in size due to the cube/square relationship of structural weight and lift, further increases in size of helicopters or multiple helicopter lift systems would involve increasingly less vertical lift capacities per pound of aircraft in the larger sizes such that further appreciable increase in size of helicopter units would be extremely expensive.
A further concept of increasing the vertical lifting capacity of two interconnected helicopters by tethering a balloon above the center of gravity of the interconnected helicopters is disclosed in U.S. Pat. No. 3,008,665. However, the high drag of the balloon coupled with the problem of coordinating movements of the independently operating helicopters makes such an arrangement impractical for most operations except at extremely low speed and over very limited ranges. The proposed arrangement could also not be used in any except ideal weather conditions of very low wind velocity and gustiness due to the inability of coordinating motion of the tethered balloon with that of each of the two independently controlled helicopters.
Lighter-than-air craft have long been advocated as mediums for the transportation of large payloads since the lifting capacity of the airship increases as the cube of the size whereas the structural increase is in the ratio of the square of the size, as the case in aerodynamically supported vehicles. However, a large aerostat is a slow responding vehicle. The hull characteristics of the conventional airship in forward flight make it unstable in both yaw and pitch. Conventional airships have no capability for developing a side force other than flying at a yawed angle nor do they have a controllable vertical lifting force other than by ballasting or valving lifting gas and flying at an angle of attack. Airships are notoriously poor in yaw controllability, particularly since the moments of inertia of even the smaller airships are many times larger than those of the largest heavier-than-air craft. The only means of controlling airships in yaw and pitch is through the rudder and elevator surfaces which have relatively small aspect ratios and are operating to a considerable extent in the boundary layer of the airship hull. At low and zero forward speeds the controllability of airships is very low, approaching zero, and the ability of a conventional airship to hold position or heading in gusty air is very poor. Thus, although a conventional airship of large size has inherent capabilities of providing large vertical lift capability, its capability of highly controlled hover flight are extremely poor. One of the requirements of the large vertical lift load carrying capability is that the carrying vehicle be capable of lifting or depositing payloads from a precise ground location and in a precisely determined alignment and azimuth. Thus, the large vertical load capacity vehicle, which must pick up and deposit the payload in the mode of the crane, must have a high degree of controllability in hover flight in addition to the ability of flying under good control at moderate speeds.
An object of this invention is to provide an airborne vehicle with the capacity of a heavy lift crane of almost unlimited payload capacity.
Another object of this invention is to provide an airborne vehicle of moderate range having a very large vertical lifting capability and capable of a very high degree of controllability in direction of motion and attitude, particularly in hover flight.
Still another object of this invention is to provide a lighter than-air craft of large size having a high degree of controllability in all flight modes but particularly in the hover flight mode.
Still yet another object of this invention is to provide a lighter-than-air craft vehicle of large payload capacity and capable of highly precise hovering flight in which its flight controllability and wind and ground handling problems are a minimum.